Technical Abstract:
Soil and landscape characteristics that influence herbicide behavior through soil/sorption and transport processes vary spatially at the scales of most agricultural fields, so it is possible that herbicide dissipation will also vary spatially. Knowledge of the spatial variability in herbicide dissipation could lead to site-specific management practices to reduce off-site transport while maintaining viable weed control. Experiments on a 6 ha watershed were conducted in order to characterize the spatial variability of isoxaflutole behavior. Spatial distribution of surface soil properties were determined for the watershed. Terrain attributes were derived from a DEM in order to ascertain if they could enhance the prediction of isoxaflutole behavior. Isoxaflutole were applied at uniform recommended rates in 2000 and 2001. At various times, soil samples were taken to a depth of 70 cm at numerous georeferenced locations having a range in soil properties representative of the site. Isoxafluole degradation to DKN was rapid and variable across the field; however DKN did not rapidly degrade between sampling times. Geostatisical analysis reveal that DKN dissipation exhibit spatial structure. The temporal spacing in the sampling events was not adequate to capture the spatial dependency of the rapid isoxaflutole dissipation. Pedotransfer functions (PTF's) reveal that for isoxaflutole, 100% of the variability was not captured with the soil properties and terrain attributes measured in this study. Elevation and % sand explain up to 40% of the variability in DKN residues across the field at two days, 1 and two weeks after application in both years. The inclusion of terrain attributes along with soil properties in PTF's improve the overall ability to predict the dissipation of isoxaflutole that could lead to specific site management.